Low penetration grade bitumen (also known as hard bitumen) is very difficult to emulsify as is well known in the art. The harder the bitumen, the lower the needle penetration value and the higher the softening point, but also the more difficult it becomes to emulsify the bitumen into storage stable, fast breaking emulsions. Low storage stability is reflected in a fast rate of separation of a water-rich upper layer and a bitumen-rich lower layer when a bituminous emulsion is stored at room temperature under quiescent conditions. The difference in water content between the layers formed is the value for the so-called storage stability, which is determined according to standard method NEN-EN 12847. Hence, the lower the value of this difference, the better the storage stability is and a value of zero indicates perfect storage stability. The storage stability is often expressed in a percentage and to obtain such percentages, the values must be multiplied by 100%.
Slow breaking of an emulsion is reflected in a long time before a solid film is formed after application of the emulsion to the road surface. It is well accepted in the art that the breaking index, or sometimes also called filler index, is a good measure for the time to break after application to a road surface. A high breaking index implies slow breaking. The breaking index is usually determined according to standard method NEN-EN 13075-1.
Storage stability can be improved by adding more emulsifier to the aqueous phase prior to emulsification. However, although improved storage stability is achieved, the breaking index also increases significantly which is obviously not desired.
A further advantage of emulsions having a low breaking index value is that these emulsions will also break relatively quickly under humid and cold conditions allowing the product to be used under less favourable environmental conditions.
U.S. Pat. No. 5,246,986 of Elf France, incorporated by reference herein, discloses an emulsion of a bituminous binder wherein a thickening agent is employed that contains at least 40% by weight of scleroglucan, wherein it is preferred that the aqueous phase of the emulsion comprises 100 to 5000 ppm, preferably 200 to 2000 ppm of scleroglucan. Examples 2 and 4 discloses cationic emulsions comprising bitumen having a penetration of 180-220 10−1 mm and scleroglucan of a technical grade (which consists of 70 wt. % of scleroglucan and 30 wt. % of biomass), wherein the scleroglucan (calculated on actual scleroglucan content) is 0.021 wt. %. The penetration was determined according to NF Standard T 66004 which is equivalent to ASTM D5-97 (cf. C. Garrigues and P. Vincent, “Sulfur/Asfalt binders for Road Construction”, “New uses of Sulfur”, Chapter 8, pages 130-153, 1975; DOI 10.1021/ba-1975-0140.ch008, Advances in Chemistry, Vol. 140, ISBN13: 9780841202184, eISBN: 9780841223219).
GB A 2452903 of Colas S. A., incorporated by reference, discloses an emulsion comprising an aqueous phase and an organic phase comprising a binder composition, wherein the binder composition comprises bitumen and a non-aromatic polymer, in particular polyisoprene. The emulsion is preferably cationic. The bitumen has preferably a penetration of 50 to 150 10−1 mm. The emulsion is rapidly breaking as indicated by a breaking index (according to NFT 66-017 (tentative French National Standard December 1983) of 45-100. The emulsion preferably comprises 45-75 wt. % of the binder composition, based on the total weight of the emulsion.
WO 2009/113854 of Latexfalt B.V., incorporated by reference herein, discloses emulsions comprising a (1→3)-β-D-glucan, preferably scleroglucan, a biodegradable emulsifier which may be non-ionic or cationic, and bitumen. The bitumen have a penetration in the range of about 10 to about 350 10−1 mm according to ASTM D5-97, more preferably about 70 to about 220 10−1 mm.
As explained above, there is a need in the art for emulsions having excellent storage stability which are fast breaking. In particular, there is a need in the art for such emulsions which incorporate low penetration bitumen (also known as hard bitumen).